The present invention relates generally to a sensor for transillumination of a blood-perfused portion of flesh to measure light extinction during transillumination, or transmissive pulse oximetry. More particularly, the present invention relates to a disposable oximeter sensor having a mechanical means for pretest of the disposable oximeter sensor and a mechanical means for improved positioning of the sensor.
Disposable oximeter sensors have been developed and used in the clinical setting for several years. During patient treatment, an oximeter sensor is used to monitor the oxygen saturation level in blood perfused tissue. Typically, oximeter sensors comprise a light source, such as a light emitting diode, a photo-sensor located such that a portion of the light emitted from the light source is received by the photo-sensor, and a means for securement to the patient. An example of an oximeter sensor has been disclosed in U.S. Pat. No. 4,830,014 granted to Goodman et al. As disclosed therein, a non-invasive, electrooptical sensor probe includes a flexible, initially substantially planar, web-like, support structure having a light source and a photo-sensor mounted in the web. An adhesive layer is further provided for removably adhesively securing the device to a portion of a patient""skin. While this type of sensor has been used in clinical settings, difficulty in positioning the sensor has been observed in practice. With an initially planar configuration and no assisting structural positioning elements, it is difficult to achieve proper alignment of the light source with the photo-sensor. Further, the optical elements present within the sensor protrude somewhat into the plane of the tape in contact with the patient""skin. Over a period of time, a dent in the skin surface may cause skin discomfort or even pressure necrosis in sensitive skin, such as that of a neonate.
Another sensor is disclosed in U.S. Pat. No. 5,217,012 granted to Young et al. The device disclosed in this patent includes a U-shaped support structure having spaced, opposed upper and lower inner surfaces. The U-shaped structure is designed to aid in pre-alignment of the device during patient use. A light source and a photosensor are mounted in the U-shaped support structure. The sensor includes means, such as adhesive, for removably securing the sensor to the skin. In practice, devices similar to that disclosed in the above-mentioned patent have proved to be predisposed to accidental closure of the U-shaped support structure upon itself, adhesive to adhesive, during application. This creates difficulty for the clinician, and nullifies the positioning feature of the U-shaped support structure taught by the Young patent.
It should be further noted that, in general, the production of disposable oximeter sensors is, by economic necessity, not of the same grade as more expensive reusable devices, such as finger clip-type sensors. This is due to the high-volume production means used-in the manufacture of disposable devices, such as the lower sampling and verification programs employed in product testing, as compared to reusable devices. However, the benefits of a disposable device, including size, application benefits, and advantages for infection control, cause the disposable product to be preferred by many health care professionals. Furthermore, despite medical quality system improvements to reduce the number of sensor failures that reach the patient care environment, the predominant type of sensor failure is xe2x80x9cout of the boxxe2x80x9d failure of newly applied sensors. This type of failure is especially problematic as it may cause a gap in patient care and loss of valuable time while the performance deficiency is investigated or a replacement sensor is located and applied. This situation may be further complicated in treating patients having compromised circulation, where readings are more difficult to obtain.
In view of the above-noted concerns, and also to present a sensor for transillumination of a blood-perfused portion of flesh that is easily positioned, minimally invasive to the patient, and able to be pretested, the present invention teaches a novel oximeter sensor. The present invention contemplates an initially L-shaped sensor having positioning elements and a removable liner. The sensor may be disposable, or for single patient use, and is designed to be affixed to any blood-perfused tissue, preferably a fingertip.
The sensor includes a flexible support structure having outer and inner surfaces, at least one positioning element, a light source, a photo-sensor, a conformal adhesive tape laminate mounted on the support structure, a leveling pad, and a removable liner. The inner surface of the flexible support structure preferably includes a biologically acceptable adhesive for adjacent retention of the adhesive tape laminate and adhesion to the skin surface while the sensor is in use.
The present invention contemplates an adhesive tape laminate, which is adhesively mounted on the adhesive coated, inner surface of the support structure. The conformational adhesive tape laminate is preferably comprised of an adhesive coated, longitudinally folded, adhesive tape. The tape laminate preferably includes an outer, light transmissive layer. The longitudinally folded tape laminate is defined by two oppositely disposed outer surfaces and two, facing inner surfaces, with a fold pocket area located between the two facing, inner surfaces. A light source and a photo-sensor are mounted in the fold pocket area in a spaced-apart configuration so that they may be positioned generally opposite each other upon mounting of the sensor to an appendage, such as a finger. One of the outer surfaces of the tape laminate is preferably provided with at least one window area. The window area is created when a portion of an inner surface is removed, leaving only the outer, light transmissive layer. At least one of the optical elements extends inwardly of the window area, thereby permitting light to pass therethrough.
The sensor according to the present invention is further provided with at least one positioning element. The positioning element is provided to cause the sensor to maintain a generally L-shape prior to use. The positioning element is preferably located in the fold pocket area of the tape laminate, at a location approximately midpoint of the laminate longitudinal length, but preferably somewhat closer to the photo-sensor. This arrangement ensures that the sensor is defined by two unequal leg portions when the sensor is in its initial L shape. However it is to be understood that the positioning element may be located at any point along the tape laminate length that will allow a generally L-shape to be imparted to the attached support structure and tape laminate. The positioning element is relatively stiff to impart an initially generally L-shape to the sensor and its cooperating elements, and permits the clinician to accurately position and apply the sensor to patient tissue up to the bend of the L, thereby locating the sensor elements in proper opposition once the device is secured in operating position. This feature overcomes the difficulties encountered with the U-shaped sensors presently in use, such as premature adhering prior to proper positioning.
The sensor of the present invention is further provided with a leveling means positioned in the fold pocket area in the marginal area surrounding at least a major portion of the optical sensor element. The leveling means is preferably a thin, deformable material such as a PVC foam tape approximately the thickness of the optical elements. The leveling means allows the sensor to conformably match the contours of the skin and helps alleviate protrusion of the optical sensor elements into the skin of the patient. This feature is of particular importance in conditions of long term monitoring in which the sensor is to be used for several days, or in which the sensor is to be applied to fragile skin, in the case of neonates. Furthermore, the leveling means provides an additional purpose in improving the seal between the skin and the optical sensor element. As a result, incident stray light that may impinge on the optical sensor element is reduced. This feature improves the sensor""performance with respect to patient motion in which stray light may produce an extraneous signal.
The present invention further contemplates an oximeter sensor having an adhesively attached liner. The liner is initially attached to the inner adhesive surface of the flexible support structure, but may be easily peeled away from the support structure to allow the sensor to be mounted to a patient appendage. The liner includes two end portions, which may be adapted to conjoin, forming a tear drop shape. When the liner presents the tear drop configuration, the light source and the photo-sensor are presented in opposition to one another allowing the clinician to test the performance of the sensor prior to removal of the liner and attachment of the sensor to the patient. Alternatively, this arrangement, in configuration with the functional liner, may be used to test the performance of the sensor at the manufacturing site, as a quality assurance prior to shipping. The liner is preferably substantially transparent to the wavelengths of light used by the sensor for interrogation of patient tissue. These features permit sensor verification and system performance evaluation prior to use, thus increasing the likelihood of successful patient monitoring.